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Tuesday, July 20, 2010

Pyramid Lake, located in northwest Nevada (MSRMaps), is named for a pyramidal-shaped tufa-mound island officially known as The Pyramid, also called Pyramid Rock. Hot water emanates from springs all around the base of The Pyramid near water level, a fact that can be tested by swimming out to the rock. Please note that the largest island in the lake, which is sometimes thought incorrectly by passers-by to be The Pyramid, is actually Anaho Island, a pelican nesting site. Although Pyramid Lake is entirely within the Paiute Indian Reservation, Anaho Island is a National Wildlife Refuge.

Anaho Island and The Pyramid as seen from an overlook near the junction of Nevada routes 445 and 446.

Anaho Island is the large island in the right and center part of the photo; The Pyramid is the small island closer to the far shore and immediately to the left of Anaho.

The Needles Rocks as seen near Thunderbolt Bay.

As you drive north of Sutcliffe, the paved road turns to dirt — variable dirt, from good conditions right after a blading, to execrable conditions of extreme and rocky washboard that will set your teeth on edge if you really want to get through to destinations to the north (Smoke Creek Desert), northeast (Gerlach and Black Rock Desert), and northwest (Honey Lake).

The Needles Rocks tufa mounds seen in the distance from the pullout at George Washington Rock.

The tufa mounds or masses known officially as "The Needles Rocks" and locally as "The Needles" and even "the Needles Rocks," form two rough lineaments near some once popular hot springs at and near the lake margin. If you back out from the MSRMaps view in aerial photo mode, you'll see that the lineaments are parallel to faults or structures cutting bedrock to the north. It seems likely that the hot springs are related to the linear structural conduits, and that both are related to the formation of the mounds, although it turns out that most or all of the large-scale tufa mounds and features formed 26,000 to 13,000 years ago when calcium-rich springs, possibly cold, emanated from the lake bottom (Benson, 2004). Some tufa may still be depositing today, especially at places like The Needles Rocks, where springs may still contain high amounts of calcium (read more here and here).

I don't personally know much about the spring-water composition, but do know that the hot springs at The Needles Rocks are great, especially the hidden ones along water's edge, where you can swim beneath tufa into warm mini-caves. This is the same view of The Needles Rocks, with a spherical tufa dome on the right. Another view from the same point at George Washington Rock (Google Street View). I was really surprised to find that Google had driven this road — it used to be considered a road going from nearly nowhere to almost nowhere else: I mean, it goes places, but it's mostly traveled by locals.

I'm not sure which of the two or three large tufa mounds or masses at this pullout is George Washington Rock; a sign may explain things — or maybe the sign just reminds you that you should have a day-use permit to pull off the main road. A nicely formed tufa dome. Go to The Pyramid to see some tufa "forts" — my word — where large, spherical domes have been eroded in half so you can see the many layers and types of tufa inside. The Stone Mother and the eroded forts uphill from her are great examples (MSRMaps location). Be prepared for a rough, though passable, drive in.Inside most of the spherical tufa domes — which are called barrels or spheroids, see Figures 18and 19, among others — you will find masses of elongate to radiating crystals of thinolite. This partially eroded tufa spheroid shows multiple layers of thinolite crystals

"Thinolitic tufas, or thinolites are thought to be chemical precipitates that originally had the composition CaCO3.6H2O; that is, they precipitated as the mineral ikaite, which suggests the presence of very cold water (Shearman and others, 1989). The thinolites have since recrystallized to a more stable form of calcium carbonate (calcite)."

The last time I was there, in June 1991, it was open to the public. I was leaning back in my camp chair, watching the sun dogs to the west, when I glanced straight overhead and saw a Kern arc. The sun was low on the western horizon, and the arc looked like a rainbow making a complete circle around the zenith. It was distinct, not faint like the one at Atmospheric Optics. At the time, I didn't even know such a thing was possible.